Laser power meter

Abstract

A laser power meter is described which enables the direct measurement of the output power of lasers over a full range of differing beam wavelengths. The laser power meter includes not only the photocell for intercepting a laser beam and the needle-scale meter conventionally provided, but also calibration means for simple adjustment of the meter to provide a correct power reading irrespective of the wavelength of the beam whose power is being measured. The calibration means includes first and second pluralities of resistors which are selectively connected in series between the photocell and the needle-scale meter by switches which are calibrated in nanometers. A user of the device is able to obtain a true reading of the power in a laser beam merely by "dialing in" the wavelength of the beam and selecting the proper power range for the needle-scale meter.

What is claimed is: 
     
       1. A laser power meter for measuring the power of a laser beam or the like over a range of output wavelengths comprising: A. sensing means responsive to the interception of the output beam of a laser by generating an electrical output potential having a value dependent upon both the power and the wavelength of said intercepted beam;   B. indicator means for registering power as a function proportional to the value of an electrical potential applied thereto; and   C. calibration means responsive to receipt of the output of said sensing means by passing an electrical potential to said indicator means; said calibration means including: 1. first and second pluralities of resistors; a. said first plurality of resistors being selected to provide first resistance values between said sensing means and said indicator means, each of which resistance values responds to the receipt by said sensing means of a laser beam having a wavelength at the starting point of a chosen one of correspondingly successive segments of said wavelength range by passing a potential to said indicator means having a value in the proximity of the potential value causing said indicator means to register the true power of a laser beam having a wavelength representative of said starting point;   b. said second plurality of resistors being divided into first and second sections respectively providing ten and unit decimal resistance value selection, said resistance values being related to successive wavelength measurement values in a straight line function having a slope which approximates the slope in all of said wavelength segments of the actual relationship of resistance values to wavelength measurement values which would cause said indicator means to register the true power of laser beams received by said sensing means having said wavelengths; and   c. said starting points of said successive wavelength segments provided by said first plurality of resistors being selected at changes in the hundreds unit of a measurement of wavelengths within said wavelength range, the relationship of successive resistance values provided by said first plurality of resistors being related non-linearly to corresponding wavelength measurement values;     2. first switching means for connecting between said sensing means and said indicator means one or more of the resistors of said first plurality of resistors to provide a selected one of said first resistance values defining a chosen one of said successive wavelength range segments; and   3. second switching means including first and second switches respectively associated with said first and second sections of resistors of said second plurality of resistors for also connecting between said sensing means and said indicator means resistors of said sections to select digitally the beam wavelength in the chosen one of said wavelength range segments to which said sensing means will respond by passing a potential to said indicator means having a value generally equal to the potential value causing a true registration by said indicator means of the power of said laser beam, whereby said calibration means is adjustable on a decimal scale to pass an electrical potential from said sensing means to said indicator means having a value proportional to the output power of a laser beam received by said sensing means, irrespective of the wavelength of said laser beam.       
     
     
       2. The laser power meter of claim 1 wherein said sensing means is a solid state photocell energy converter. 
     
     
       3. The laser power meter of claim 1 wherein said indicator means is a meter having a reading range which is a segment of a full power range desired for said indicator, and range selector switching means are provided for selectively connecting differing resistance values in shunt with said sensing means for matching the electrical potential output of said sensing means to said meter range segment. 
     
     
       4. The laser power meter of claim 1 further including an output socket for directing the electrical potential output of said calibration means to an external indicator, and an isolation impedance connected between said output socket and said calibration means for preventing any external indicator connected with said socket from materially affecting the operation of said calibration means. 
     
     
       5. The laser power meter of claim 1 wherein there are nine resistors in each of said first and second sections to provide two successive decades of resistance value selection, each unit of which is representative of an output beam wavelength in each wavelength range segment selectable by said first switching means. 
     
     
       6. The laser power meter of claim 1 wherein said first switching means and said first and second switches of said second switching means are dialing switches manipulatable by an operator of said power meter to dial in the wavelength in nanometers of a laser beam whose power is to be measured.